Apparatus and method for forming can bottoms

ABSTRACT

A can bottom forming assembly for forming the bottom wall of a can body. A bodymaker punch urges a can bottom wall first against an outer forming ring, then against a middle forming ring, and then against a domer die.

The present invention relates generally to apparatus for doming thebottom walls of cans and, more particularly, to apparatus for domingthin walled aluminum can bodies of the type having a cylindrical sidewall and an integrally formed bottom wall.

Metal containers such as cans which are adapted to hold contents underpressure are often provided with a upwardly extending dome in the bottomwall thereof to resist the tendency of the bottom wall to deformexcessively under pressure and also to provide a generally planarannular portion at the periphery of the bottom wall which provides astable support base for the can. Numerous domed containers are describedin prior art patents such as U.S. Pat. No. 1,963,795; 3,904,069; and4,037,752 which are hereby incorporated by reference.

In doming the bottom of relatively thin walled metal cans, such asconventional aluminum beer cans, a continuing problem has been theformation of radically extending crease lines in the domed portion ofthe can. These crease lines are probable formed as a result ofnon-uniform deformation of the can bottom wall at the time it isinitially contacted by a dome-shaped die assembly. The non-uniformdeformation may be due to the fact that the die assembly initially makesa point contact at the center of the can bottom resulting in an initialdeformation of the can bottom into a conical configuration. It is in thetransition of the can bottom from a generally planar shape to such aconical shape that radial creasing of the can bottom takes place. Such acreased dome configuration is generally known in the art as a "flowerdome." A problem with flower dome formation, other than the generallyaesthetically unacceptable appearance, it that the crease lines mayrupture or weaken the can bottom and may cause leaks or non-uniformdeformation of the can bottom when the can is pressurized. Anotherproblem associated with dome formation in integrally formed thin walledcan bodies is that the deformation of the can bottom wall during domingtends to cause metal flow from the can lateral side wall to the canbottom wall resulting in a slight axial shortening of the can. One priorart technique for eliminating these problems has been to tightly engagea peripheral portion of the can bottom wall and a lower portion of thecan side wall between a bodymaker punch assembly and a pressure ringduring dome formation. Such a peripheral engagement of the can walltends to stabilize the bottom wall circumferentially, thereby reducingthe tendency of the bottom wall to crease during dome formation. Such aperipheral engagement also tends to limit the flow of metal from the canside wall to the can bottom wall. Another prior art method, sometimesused in combination with a pressure ring, for eliminating flower domeformation is application of relatively high pressure to the domed regionof the bottom wall during dome formation to "iron out" any creases thatmay have been formed during the initial portion of the doming operation.A problem with the former technique is that, in applying sufficientpressure to the periphery of the can bottom to prevent the undesirableeffects of can shortening and flower dome formation, the engaged portionof the can bottom is sometimes damaged by the pressure ring. A problemwith "ironing out" radial creases is that the ironed out creased areahas different strength and deformation characteristics than the otherportions of dome. Furthermore, such ironing out techniques are notalways successful in removing all of the radial creases.

According to the present invention there is provided an apparatus forforming a can bottom configuration in an aluminum can body of the typecomprising a generally cylindrical sidewall terminating in an open topend and a generally flat, circular bottom wall connected with thecylindrical sidewall by an inwardly tapering annular portion in whichthe bottom wall configuration to be formed comprises a peripheral ringportion extending downwardly and inwardly from said can body sidewall; arelatively small radius, downwardly convex support ring portionintegrally connected to said peripheral ring portion for supporting thecan constructed from the can body on an underlying base surface; agenerally vertically extending riser ring portion integrally connectedto said support ring portion and extending upwardly therefrom; and anupwardly projecting dome portion integrally connected to said riser ringportion, said formed bottom configuration being adapted to nest within acan end provided on a can identical to and situated below a canconstructed from said can body for enabling stable stacking of suchcans, the apparatus comprising:

(a) an axially, reciprocally movable punch means insertable within thecan body in engagement with the interior bottom surface thereof forurging the can body in a first axial direction against die means forforming the can bottom configuration, said punch means comprising asurface portion conforming generally to the configuration of the canbottom peripheral ring portion, the can bottom support ring portion andthe can bottom riser portion;

(b) die means for coacting with said punch means to form said can bottomconfiguration, said die means comprising:

i) an axially reciprocally movable outer die ring means for forming anouter portion of said can bottom configuration, having a can bodyengaging surface conforming generally to said can bottom peripheral ringportion and an outer portion of said can bottom support ring portion;

(ii) an axially reciprocally movable middle die ring means for forming amiddle portion of said can bottom configuration, positionedconcentrically with and inwardly of said outer die ring means and inclosely adjacent relationship therewith, said middle die ring meanshaving a can body engaging surface conforming generally to an innerportion of said can bottom support ring portion, said can bottom riserportion and an outer annular portion of said can bottom dome portion;and

iii) a relatively fixed, inner die means for forming an inner portion ofsaid can bottom configuration, positioned concentrically with said outerdie ring means and said middle die ring means and located inwardly ofsaid middle die ring means in closely spaced, adjacent relationshiptherewith; said inner die means having a can body engaging surfaceconforming generally to an inner portion of said can bottom domeportion.

The invention will now be described with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic cross sectional elevation view of a prior art candoming assembly.

FIG. 2 is a bottom view of a domed can bottom having radial crease linestherein.

FIGS. 3 through 6 are schematic cross sectional elevation views of a candoming assembly of the present invention showing various operatingpositions thereof.

FIG. 7 if a detailed cross sectional elevation view of a portion of aforming ring of the type illustrated in FIGS. 3 through 6.

FIG. 8 is a bottom view of a domed can bottom of the type formed by theapparatus illustrated in FIGS. 3 through 7.

FIG. 9 is a cross sectional elevation view of the domed can bottom ofFIG. 8.

FIGS. 10-13 are schematic cross sectional views of another embodiment ofa can bottom forming apparatus of the present invention showing variousoperating positions thereof.

FIG. 14 is a cross sectional elevation view of a can bottom configuratonformed by the apparatus of FIGS. 10-13 and further illustrating thenesting arrangement of that can bottom configuration with an associatedcan end.

A can doming device of the prior art is represented schematically inFIG. 1. A can body 10 to be domed has an open top end 11 defining acircular opening, a cylindrical side wall 12 and a closed circularbottom wall 14 integrally connected to the side wall at a relativelysmall radius annular shoulder portion 13. The can body 10 is mountedabout an axially extending cylindrical bodymaker punch 20 ofapproximately the same external diameter as the internal diameter of thecan. The bodymaker punch is in turn mounted don an axially extending ram16 as by a bolt 18. The bodymaker punch and the can 10 mounted thereonare axially reciprocally movable by ram 16 in a first horizontaldirection 22 and a second opposite horizontal direction 24. Thebodymaker punch 20 comprises an annular peripheral rim portion 26defined by an interior cavity 28 provided at the terminal end of thebodymaker punch 20. Rim portion 26 has a rounded terminal end portion 30which engages an interior peripheral portion 32 of the can shoulder 13and bottom 14. Bodymaker punch 20 urges the can bottom and shoulderagainst external pressure ring 40 and, subsequently, urges the canbottom against stationary domer die 50 as the ram moves in direction 22.The external pressure ring 40 which engages the can body 10 has an innerperipheral recessed ring portion defined by an inwardly facing concavesurface 42 adapted to, ordinarily, nondeformingly engage an outerperipheral portion of the can bottom 14, can shoulder 13 and a lowerportion of side wall 12. The external pressure ring 40 is mounted on aplurality of biasing air cylinders 44 which enable the pressure to bemoved with can body 10 in the direction 22 as the can bottom 14 movesfrom an initial engagement position A to a position B associated withmaximum ram movement in direction 22. Pressure ring 40 has a centralcylindrical opening 44 defined by interior surface 46 which is adaptedto receive domer die 50 in close sliding relationship therewithin. Domerdie 50 is fixedly mounted on a stationary base surface 56 and remainsstationary throughout the doming operation. Domer die 50 has a generallycircular sidewall surface 52 and terminates in a constant radiusdome-shaped, sometimes herein referred to as "spheroid," end surface 54.As the can engages stationary domer die 50 during its movement indirection 22, the domer die end surface 54 engages the bottom wall 14forcing it into a dome-shaped configuration 58, shown in phantom, ofsubstantially the same shape as the terminal surface 54 of the domer die50. An outer generally flat surfaced peripheral bottom ring 60 is alsothus provided in the bottom wall by the doming operation. Bottom ring 60provides a stable support base for the can.

Earlier can doming assemblies did not include an external pressure ring40. However such earlier can domers produced undesirable radiallyextending creases 62, 64, 66 etc., in the domed can bottom asillustrated in FIG. 2. Such a creased dome bottom is known in the art asa "flower dome." Such crease formation is aesthetically undesirable andalso weakens the domed can bottom. Another undesirable effect of suchdoming without an external pressure ring is that metal in can body sidewall 12 tends to flow into the dome region 58 as it is being formedthereby shortening the axial length of the can body 10. It was toovercome the effects of can shortening and flower dome formation thatpressure rings such as shown in FIG. 1 were introduced. The pressurering 40 engages the bottom periphery of the can body prior to the can'sengaging the stationary domer die 50. The pressure ring appliessufficient pressure against the engaged portion of the can body to limitthe metal flow conditions associated with can shortening and, to someextent, stabilizes the can bottom circumferentially to prevent flowerdome formation. Although such an external pressure ring 40 may berelatively effective in preventing flower dome formation and canshortening, it has been found that in many cases the biasing pressurewhich must be applied by the pressure ring against the can bottom toprevent such problems may itself be damaging to the engaged portion ofthe can bottom.

The can doming assembly 100 of the present invention also preventsflower dome formation and can shortening but is much less likely todamage the lower portion of a can than prior art pressure rings.

As illustrated by FIGS. 3 through 6, the can doming die punch assembly100 of the present invention is adapted for operating on a can body 110of a type having an open top end 111, a cylindrical side wall 112, agenerally flat bottom wall 114, and a relatively short length sortradius annular shoulder 113 connecting the side wall and bottom wall.The can doming die punch assembly 100, in general, comprises a bodymakerpunch 120 mounted as by a bolt 118 on a reciprocating ram unit 116adapted to reciprocally move in a first horizontal direction 122 towardsa domer die 180 and a second opposite horizontal direction 124 away fromthe domer die; a forming ring 140 adapted to formingly engage aninwardly positioned annular band portion 187 of the bottom wall 114 toprovide a peripheral portion 203 of a dome 201 to be formed in the canbottom wall; and a fixed domer die 180 adapted to engage a centralcircular portion 189 of bottom wall 114 to form an inner dome portion208 of the dome 201 to be formed in bottom wall 114; and biasing meanssuch as air cylinders 194, 196 adapted to provide a constant relativelylow biasing pressure in a direction 124 as the forming ring 140 moves indirection 122 during can dome formation.

In operation ram 116 and attached bodymaker punch 120 move can body 110in direction 122 from an initial position in spaced relationship fromforming ring 140 and domer die 180 as shown in FIG. 3. Can bottom wall114 is initially engaged by annular surface 144 of forming ring 140. Ram116 and bodymaker punch 120 subsequent to engagement of bottom wall 114by surface 144 continue moving in direction 122 while forming ring 140initially remains in a fixed position. The continued movement of thebodymaker punch and associated can 110 thus cause deformation of the canbottom 114 in the area engaged by the forming ring 140. Forming ring 140remains relatively fixed until the bodymaker punch 120 and can body 110have moved into the position illustrated in FIG. 4 wherein the outerperipheral portion of the can bottom is forced into engagement with aradially outer peripheral portion of forming ring surface 144.Thereafter further movement of the bodymaker punch 120 is accompanied bymovement of the forming ring 140 in the same direction (122) and at thesame relative rate. As illustrated in FIG. 5 this downward movement offorming ring 140 causes the central portion of the can bottom 114 tosubsequently be engaged by an upper dome-shaped surface 186 of domer die180. Subsequent movement to a position illustrated in FIG. 6, whichrepresents the furthest extension of ram 116 in direction 122, causesthe can bottom 114 to be further deformed by the domer die 180 tocomplete the formation of a dome 201 having a relatively constant radiusand composed of a first dome portion 203 formed by the forming ring 140and a second portion 208 formed by the domer die 180. Having thusdescribed the invention in general further specific features of theinvention will now be described.

As illustrated in FIGS. 3 through 7, forming ring 140 comprises anannular can bottom engaging portion 142 having an outwardly facinggenerally outwardly convex can bottom engaging annular surface 144. Theforming ring also comprises an internal cylindrical surface 146 adaptedto slidingly accept the domer die 180 therewithin; and a recessedannular fluid discharge ring 148 adapted for collecting lubricatingfluid and gases trapped between the can bottom 114 and various surfaceof the forming ring and domer die and having associated therewithaxially extending fluid discharge passages 150, 152, etc. for expellingsuch collected fluids. The forming ring also comprises an outer bodyportion 154 having a cylindrical outer surface 156 and a pair ofoppositely radially extending surfaces 158, 160. As illustrated in FIG.7 the outwardly facing generally convex can bottom engaging annularsurface 144 may include a generally planar radially extending surfaceportion 162 extending perpendicular to the direction of ramreciprocation and associated with an outer peripheral support ringportion 202 of the can bottom 200 being formed. Surface 144 alsocomprises an outwardly facing, concave, relatively short length, smallradius (0.05 in.), annular transition surface portion 164 which isassociated with a can bottom transition surface 204 and which connectssurface 162 to an outwardly facing, relatively large radius (.219 in.),convex surface portion 166 which is associated with a peripheral portion203 of the can dome 201 to be formed. Surface 166 is integrallyconnected to axially extending cylindrical surface 146 by radiallyinwardly facing, small radius (0.05 in.), convex shoulder portion 168.

Domer die 180 which is positioned in axially aligned relationship withbodymaker punch 120 comprises a main cylindrical body portion 182,having a cylindrical side wall 184 having a diameter, e.g., 1.736 in.,about 30% less than the can body diameter, e.g. 2.50 in. and a domeshaped terminal end surface 186 which may have a radius approximatelyequal to the can diameter, e.g. 2.50 in., Domer die 180 also comprises abase portion 188 having a radially extending surface 190 affixed to asupport surface and opposite radially extending surface 192 connected bya outer cylindrical wall portion 195. Biasing means such as aircylinders 194, 196 may have barrel portions 191, 193 mounted in recessedportions of the radially extending base portion 188 and may have pistonportions 197, 199 attached to outer radial portions of forming ring 140.The air cylinders 194, 196, etc. having central longitudinal axes CC, DDextending parallel to the central longitudinal axis AA of the bodymakerpunch 120 and domer die 180. Of course the biasing air cylinders 194,196 may be replaced by conventional biasing springs or other biasingmeans. A surprising feature of the can doming die punch assembly 100 ofthe present invention is that the pressure exerted by the forming ringsurface 144 against the can bottom during doming may be significantlyless, approximately an order of magnitude less, than the pressureexerted by a conventional pressure ring 40 against an associated canbottom during dome formation by conventional prior art techniques. Forexample, in the formation of a conventional aluminum beer can having adiameter of approximately 2.50 inches, a force of approximately 50 lbs.on the can bottom wall is sufficient to prevent axial can shortening andflower dome formation when using a can doming die punch assembly 100 ofthe present invention; whereas a force of approximately 900 lbs. must beexerted by a conventional pressure ring 40 against a can bottom toprevent axial shortening and flower dome formation. Thus the presentinvention is much less likely to damage a can bottom than prior artapparatus such as described in FIG. 1.

Another embodiment of the invention is illustrated in FIGS. 10-14. Inthis embodiment, the invention comprises an apparatus 300 for forming acan bottom configuration 301 in an aluminum can body 10' of the typecomprising a generally cylindrical sidewall 12' terminating in an opentop end 11' and comprising a generally flat, circular bottom wall 14'integrally connected with the cylindrical sidewall by an annular taperedportion 13'. As shown in FIG. 14, the bottom wall configuration 301 tobe formed comprises a peripheral ring portion 302 extending downwardlyand inwardly from the can body sidewall 12'; a relatively small radius,downwardly convex support ring portion 304, integrally connected to theperipheral ring portion 302, for supporting the can 10A constructed fromthe can body 10' on an underlying base surface; a generally verticallyextending riser ring portion 306, integrally connected to the supportring portion and extending upwardly therefrom; and an upwardlyprojecting dome portion 308 integrally connected to the riser ringportion 306. The formed bottom configuration 301 is adapted to nestwithin a can end 310 having a flat, circular base portion 312, anintegrally formed peripheral rim portion 314, and a centrally positionedpull tab 316 which is provided on a can 10B identical to and situatedbelow the can 10A constructed from the can body 10' for enabling stablestacking of such cans.

As shown in FIG. 10, the apparatus 300 comprises an axially,reciprocally movable punch means 320 insertable in close slidingrelationship within the can body 10' in engagement with the interiorbottom surface 322 of the can body for urging the can body in a firstaxial direction 324 against a die means 326 for forming the can bottomconfiguration 301. The punch means comprises a surface portion 328conforming generally to the configuration of the can bottom peripheralring portion 302, the can bottom support ring portion 304 and the canbottom riser portion 306.

The apparatus comprises die means 326 for coacting with the punch means320 to form the can bottom configuration 301. The die means 326comprises an axially reciprocally movable outer die ring means 330 forforming an outer portion of the can bottom configuration 301. The outerdie rings means has a can body engaging surface 332 conforming generallythe configuration of the can bottom peripheral ring portion 302 and anouter portion of the can bottom support ring portion 304.

The die means 326 further comprises an axially reciprocally movablemiddle die ring means 336 for forming a middle portion of the can bottomconfiguration 301. The middle die ring means 336 is positionedconcentrically with and inwardly of the outer die ring means 330 inclosely adjacent relationship therewith. The middle die ring means 336has a can body engaging surface 338 conforming generally to theconfiguration of an inner portion of the can bottom support ring portion304, the can bottom riser portion 306 and an outer annular portion ofthe can bottom dome portion 308.

The die means 326 also comprises a relatively fixed, inner die means 342for forming an inner portion of the can bottom configuration 301. Theinner die means 342 is positioned concentrically with the outer die ringmeans 330 and the middle die ring means 336 and located inwardly of themiddle die ring means in closely spaced, adjacent relationshiptherewith. The inner die means 342 has a can body engaging surface 344conforming generally to the configuration of an inner portion of the canbottom dome portion 308.

As illustrated in FIGS. 11 and 13, the outer die ring means is biased ina second axial direction 325 opposite the first axial direction 324 by aplurality of springs 350 or other biasing means such as air cylinders(not shown). Biasing means such as springs 352 are also provided forbiasing middle die ring means 336 in axial direction 325. Biasing means350 supports the outer die ring means 330 above a support base surface354 in a relatively elevated position with respect to the middle diering means 336 and inner die means 342 when the outer die ring means 330is otherwise unloaded. Springs 352 similarly support the middle die ringmeans 336 in elevated position above the inner die means 342 when themiddle die ring means 344 is ohterwise unloaded. The elevation of theuppermost surface portion 360 of outer die ring means 330 may be, e.g.,0.4 inches above the uppermost surface portion 362 of middle die ring336, and the uppermost surface portion 362 of the middle die ring means336 may be, e.g., 0.1 inches above the uppermost surface portion 364 ofthe inner die means 342.

In operation, as illustrated in FIG. 10, a can body 10' mounted on punchmeans 320 makes initial contact with the outer die ring means 330 attapered portion 13' thereof as the punch means moves in axial direction324. The chamfered portion of outer die ring means 330 which providesthe can engaging surface 332 has a maximum diameter at the uppermostportion thereof which is slightly larger, e.g. 0.2 inches, than thediameter of the can body sidewall portion 12'.

As shown in FIG. 10, at the time of initial engagement, only can bodytapered portion 13' makes contact with the die means 326, and onlynominal deformation of the can body takes place at this time due to therelatively low bias force provided by outer die ring biasing meanssprings 350 and the relatively high structural integrity of the can bodyin tapered region 13'. As the punch means 320 moves downwardly, engagedouter ring portion 330 moves downwardly at approximately the same rate.As illustrated in FIG. 11, the can bottom next makes contact with themiddle die ring means 336 which immediately begins to deform the canbody bottom wall 14' due to the relatively greater biasing forceprovided by springs 352 than that provided by springs 350, and also dueto the fact that the mid-portion of the can bottom has less structuralintegrity than the can tapered portion 13'. As the punch means 320 movesdownwardly from this point, the outer die ring means 330 movesrelatively more in direction 324 than the inner die ring means 336 andthe punch means 320 moves relatively more than the outer die ring means330, thus initiating the formation of the can bottom peripheral ringportion 302, support ring portion 304, and riser portion 306, as well asan outer portion of the can bottom dome portion 308, prior to contactingengagement between the can body bottom wall 14' and the inner die means342, as illustrated in FIG. 12. As illustrated in FIG. 13, subsequent tocontact of the can bottom wall with the inner die means 342, furtherdownward movement of the punch means 320 produces formation of the innerportion of the can bottom dome portion 308 and causes completion of theother portions of the can bottom configuration 301. At the position ofgreatest movement in direction 324, as shown in FIG. 13, punch means 320has urged the associated portions of the die means 326 into arelationship such that the can body engaging surface 332, 338, and 344are aligned to define a substantially continuous can engaging surfacewhich is substantially identical to the configuration of the can bottomconfiguration 301 which is to be formed by the apparatus. In a preferredembodiment, this alignment position occurs when the outer die ring means330 and the middle die ring means 336 are bottomed-out against theirassociated stop surfaces 354 and 355.

As illustrated in FIG. 14, the can bottom configuration 301 which isformed provides a nesting configuration with an associated can end 301mounted on a can 10B positioned below the bottom configuration 301 inwhich the support ring portion 304 of the can bottom is positionedimmediately inwardly of the can end peripheral rim portion 314 and inwhich the riser portion 306 has a sufficient dimension to elevate thecan bottom dome portion 308 into non-interfering relationship with thepull-tab portion 316 of the can end 310. Stackable can configurationssuch as illustrated in FIG. 14 are known in the art.

We claim:
 1. An apparatus (300) for forming a predetermined can bottomconfiguration (310) in a can body (10') having a cylindrical sidewall(12') and an integrally formed bottom wall (14') characterized by(a)punch means (320) insertable within the can body (10') in engagementwith the interior bottom surface (322) thereof for urging the can bodyagainst die means (326), (b) die means (326) for coacting with saidpunch means (320) to form said can bottom configuration comprising:(i)axially reciprocally movable outer die ring means (330) for forming anouter portion of said can bottom configuration (301); (ii) axiallyreciprocating movable middle die ring means (336) for forming a middleportion of said can bottom configuration, said outer die ring meansbeing positioned in encompassing adjacent relationship with said middledie ring means; and (iii) inner die means (342) for forming an innerportion of said can bottom configuration; said middle die ring means(336) being positioned in encompassing adjacent relationship with saidinner die means (342).
 2. Apparatus according to claim 1, characterizedin that said die is constructed and arranged whereby said outer die ringmeans (330) makes the first contact with a can bottom, said middle diering means (336) makes the second contact with the can bottom, and saidinner die means makes the third contact with said can bottom. 3.Apparatus according to claim 2, characterized in that said punch means(320) is reciprocally movable; said inner die means (342) being fixed.4. Apparatus according to claim 3, characterized in that said outer diering means (330) and said middle die ring means (336) are adaptedyieldingly to resist movement of said can body (10') in a first axialdirection (324).
 5. Apparatus according to claim 4, characterized inthat the initial resistance force applied against said can body (10') bysaid middle ring means (336) is greater than the initial resistanceforce applied against said can body by said outer die ring means (330).6. A method for forming a predetermined can bottom configuration (301)in a can body (10') characterized by the steps of:(a) urging the bottomwall of the can body against a first yieldingly resisting die ring(330); (b) while the bottom wall is still in engagement with the firstdie ring (330), urging it against a second yieldingly resisting die ring(336) positioned radially inwardly of the first die ring (330); (c)while the bottom wall is still in engagement with the first and seconddie rings (330, 336) urging it against a central die portion (324)positioned radially inwardly of the second die ring; and (d) continuingto urge the bottom wall against the first and second die rings and thecentral die portion until a bottom wall configuration having a firstbottom wall portion conforming to the shape of the first die ring, asecond bottom wall portion conforming to the shape of the second diering, and a third bottom wall portion conforming to the shape of thecentral die portion is formed.